Terephthalic acid/p,p-sulfonyldibenzoic acid/ethylene glycol/neopentyl glycol polyester compositions and containers made therefrom

ABSTRACT

Copolyesters having an oxygen permeability of less than 15 cc. mil/100 in. 2  ·day·atm. (at 50% relative humidity and about 73° F.) and a glass transition temperature in excess of 72° C. and having the following four (4) repeating units are contemplated: ##STR1## Based on reactant charges the ratio of (b) units: (a) units will be about 90:10 to about 40:60. Containers made of these polyesters for packaging products of commerce like comestibles are also contemplated.

BACKGROUND OF THE INVENTION

The present application is directed to prescribed polyester compositionsand more specifically to copolyester compositions; additionally, thepresent application is directed to packaging methods and containersfabricated of these polyesters.

Packages, such as bottles, and their method of preparation, made ofpolyethylene terephthalate are disclosed in U.S. Pat. No. 3,733,309.These packages are biaxially oriented bottles and are disclosed to bemanufacturable from a homopolymer of ethylene glycol and terephthalicacid or copolymers of ethylene terephthalate wherein up to 10 molepercent is prepared from the monomer units of for example diethyleneglycol, propane-1,3-diol, butane 1,4 diol, 1,4-hydroxymethylcyclohexane,isophthalic acid, and the like. While bottles from the polyethyleneterephthalate have quite satisfactory permeability characteristics whichallow them to be used for packaging various products of commerceespecially comestible items including foodstuffs, or medicines, theyneed improvement in order to allow them to satisfactorily withstandhigher temperatures. Generally, as indicated above, the permeabilitycharacteristics of polyethylene terephthalate are satisfactory andtypically an unoriented polyethylene terephthalate will have an oxygenpermeability of around 8-10 cc.mil/100 in.² ·day·atm. and a CO₂permeability of around 48 or 50. The glass transition temperature ofpolyethylene terephthalate, however, is on the order of about 72° C.and, whether a container made therefrom is unoriented or biaxiallyoriented, it will be realized that a higher glass transition temperatureis needed in order to allow a container thereof to withstand highertemperatures. Thus a need exists for a polyester container which iscapable of withstanding higher temperatures, for example, thoseencountered in an autoclaving procedure and even the temperatures quitefrequently existing in warehouses, than PET.

As will be subsequently seen, the present invention provides containersof prescribed copolyesters which polyesters have glass transitiontemperatures in excess of 72° C. and which have satisfactory oxygenpermeability characteristics thus making them ideally suited for formingoriented or unoriented containers or bottles and for the packaging ofvarious products of commerce; additionally, these polyesters have theneeded balance of properties to allow them to be melted and expedientlyformed into containers and the present copolyesters have decompositionpoints which are above normal processing temperatures so as not to causeany significant discoloration problems when synthesizing the compositionand manufacturing bottles and packages therefrom.

While not directed to bottles, U.S. Pat. No. 3,862,084 mentions thehomopolymer of ethylene glycol and terephthalic acid, as well ascopolyesters from terephthalic acid and/or one or more different acids,e.g. isophthalic acid, and from ethylene glycol and/or one or moredifferent alcohols, such as, neopentyl glycol, that is 2,2-dimethyl1,3-propane diol.

A wide variety of copolyester compositions are known in the prior art.U.S. Pat. No. 3,522,215 discloses a composition formed from terephthalicacid, 1,4-cyclohexane dimethanol and a third, broadly disclosed,dicarboxylic acid (or ester) component which may, for example, bep,p'-sulfonyldibenzoic acid or p,p'-isopropylidenedibenzoic acid; as afourth component, another acid or glycol can be used; the glycolsdisclosed include ethylene glycol, ether glycols, and branched glycolsand carbocyclic glycols with neopentyl glycol (i.e., 2,2-dimethyl1,3-propane diol) being set forth as a branched chain glycol. U.S. Pat.No. 3,547,888 discloses compositions formed from terephthalic acid (orits ester), 1,4-cyclohexane dimethanol and, for example,p,p'-sulfonyldibenzoic acid or p,p'-isopropylidenedibenzoic acid (oresters); reference may also be had to 78 Chemical Abstracts 160332y andGerman Offenlegungsschrift 2,146,055.

U.S. Pat. No. 2,744,094 discloses polyesters formed fromp,p'-sulfonyldibenzoic acid (or its esters or acid chloride) plus anaromatic dibasic acid diester, and a polymethylene glycol, and/or analiphatic ether glycol, and indicates that mixtures of straight chainalkane diols or ether glycols may be employed. U.S. Pat. No. 2,744,097discloses polyesters from beta-hydroxyalkyl diesters ofp,p'-sulfonyldibenzoic acid and dihydroxy compounds, for example,aliphatic ether glycols, and polymethylene glycols. U.S. Pat. No.2,744,088 discloses polyesters of p,p'-sulfonyldibenzoic acid (or estersor acid chlorides), an aliphatic straight-chain dibasic acid, or esterthereof, and an alkylene glycol and/or aliphatic ether glycol; branchedchain glycols are mentioned and ethylene glycol and neopentyl glycol(2,2 dimethyl-propane diol-1,3) are specifically set forth. Theforegoing patents are discussed in Vol. 50 Chemical Abstracts, col.16183 and other polyesters from p,p'-sulfonyldibenzoic acid arediscussed in cols. 16180-16182.

U.S. Pat. No. 2,901,466, somewhat similar to some of the above patents,discloses linear polyesters formed from 1,4-cyclohexanedimethanol andone or more hexacarbocyclic dicarboxylic acids (or its ester or halide),e.g. p,p'-sulfonyldibenzoic acid, isophthalic acid, terephthalic acid;modifying glycols, e.g., ethylene glycol, ether glycols, neopentylglycol (2,2'-dimethyl-1,3-propanediol), and carbocyclic glycols are alsoindicated.

German Offenlegungsschrift 2,140,615 and Chemical Abstracts, Vol. 78148445e describe a linear polyester having a glass transitiontemperature of about 145° C. to about 163° C. which is made fromethylene glycol, neopentyl glycol (2,2'-dimethyl-1,3-propanediol) andbis(4-butoxycarbonylphenyl) sulfone (butyl ester ofp,p'-sulfonyldibenzoic acid).

Recently issued U.S. Pat. No. 3,890,256 discloses polyesters formed fromneopentyl glycol but indicates that, for its purposes of producing highimpact and high tensile strength, such a glycol is unsatisfactory.

British Specification 962,913, and its Addition Patent 1,044,015, andFrench Brevet 1,456,345 disclose linear polyesters, optionally alongwith another glycol formed from 2,2, 4,4-tetramethyl 1,3-cyclobutanediol. Polyester forming acid reactants include terephthalic acid,isophthalic acid, and p,p'-sulfonyldibenzoic acid. Ethylene glycol andneopentyl glycol, as possible modifying alcohols, are indicated in allthree documents. Thus, as will be seen from the foregoing, an extensiveamount of work has been done with polyesters but little has been done tosatisfy the needs of the packaging industry for an improved polyestercontainer composition suitable for the packaging of various products,especially comestibles like foodstuffs or medicines, and the like. Thatis, no one has focused their attention on satisfying the need forproviding a packaging container of a linear polyester havingsatisfactory oxygen permeability characteristics and a glass transitiontemperature higher than polyethylene terephthalate.

Thus in accordance with the present invention there is provided animproved polyester which can be melted and molded to a clear containerfor use in the packaging industry wherein the repeating units of thepolyester, or the radicals remaining after transesterification, oresterification, and polycondensation consists essentially of (a), (b),(c), and (d) wherein ##STR2## The polyesters contemplated herein have anoxygen permeability as measured by ASTM D-1434-66 of less than 15cc.mil/100 in.² ·day·atm. and a glass transition temperature in excessof about 72° C. The mole ratio, based on the amounts of the reactants,i.e. the polyester forming precursor, used in the reaction, of the (b)units above to the (a) units above will be between about 90:10 and about40:60 and the ratio of the (c) units above to (d) units above will beabout 80:20. Generally the precursors of the (a) and (b) units as wellas the (d) and (c) units react to form the polyesters in about the molarproportion used in the synthesis of the polyester.

The polyesters contemplated herein, and perhaps more accuratelycopolyesters, are the polyester products wherein units (a) are obtainedfrom a polyester forming precursor which is p,p'-sulfonyldibenzoic acid,esters thereof, or acid halides thereof, and wherein the (b) units areobtained from terephthalic acid, esters or acid halides thereof. Units(c) and (d) above are, respectively, obtained from polyester formingprecursors which are ethylene glycol and neopentyl glycol(2,2-dimethyl-1,3-propanediol).

Unit (b) above will be the radical obtained from a polyester formingprecursor which is terephthalic acid, its esters, or halides, and themole ratio of (b) units to (a) units will be between about 90:10 and40:60 based on the mole ratio of the (b) and (a) precursors used for thereaction. An especially suitable linear copolyester for use in thepackaging industry is a copolyester in which the (b) units indicatedabove are the radicals obtained from a precursor which is terephthalicacid, its esters, or halides, and wherein the ratio, based on thereactant proportions, of (b) to (a) units is about 50:50 and the ratioof (c) units to (d) units is about 80:20.

The esters contemplated above as the polyester forming precursor may beany of the well known esters e.g. aliphatic esters, or aromatic esters.Preferred aliphatic, or acyclic, esters are the alkyl esters having from1 to about 4 carbon atoms with the methyl or ethyl esters beingespecially preferred. The phenyl esters are preferred aromatic esters.Instead of using the acid or esters, acid halides may likewise beemployed with the acid chloride being quite suitable. Thus for exampleunits (a) may be the polymerization radical obtained fromp,p'-sulfonyldibenzoyldichloride and units (b) the polymerizationradical obtained from terephthaloyldichloride.

The polyesters as contemplated herein may be synthesized by methodsgenerally known in the art for producing polyesters wherein at least onepolyester-forming dicarboxylic acid, ester, or halides thereof, isreactively combined with at least stoichiometric amounts of at least onepolyester-forming dibasic alcohol under conditions of temperaturepressure and catalysis as to form the polyester. In the usual procedurethe method of reactively combining the acid, acid ester, or acid halidewith the dibasic alcohol is a two-step process involving atransesterification step, or esterification step depending on thestarting materials, followed by a polycondensation step with thereaction being done in a melt condition. Temperatures employed whichwill be quite suitable for forming the present polyesters will bebetween about 200° or 210° C. up to about 300° C. or so. Additionally inthe usual procedure a stoichiometric excess of glycol will be employed,with the mole ratio of ethylene glycol to neopentyl glycol being about80:20. Generally the amount will be between about 2 to about 3 moles oftotal glycol per mole of total dicarboxylic acid, or ester, or halide,employed with a quite convenient amount being about 2.5 moles.

Conventional catalysts are likewise employed. For exampletransesterification is effected in the presence of effective catalyticamounts of transition metal compounds, alkaline earth metal compounds,or alkali metal compounds, for example the acetates, oxides, phenoxides,and alkoxides. Specific suitable catalysts will be, for example, zincacetate manganese acetate, magnesium acetate, and calcium acetate, andtitanium alkoxides like titanium tetrabutoxides. Suitablepolycondensation catalysts include for example antimony acetate,antimony trioxide, titanium alkoxide, and organotinoxides, for examplestannous alkoxides. Usually the catalysts will be present in an amountof about 10⁻⁵ to about 10⁻³ moles of catalysts per mole of total acid,ester, or halide employed.

In performing the reaction the reactant proportions, of course, will beselected as indicated previously. Additionally as previously indicatedunits (a) and (b) of the polyester are, relative to themselves, presentin about the same ratio as that of their precursors in the reactioncharge. Similarly the ratio of (d) to (c) units will be about the sameas the molar ratio used in the reaction for their precursors.

The present invention also contemplates an improvement in methods ofpackaging products wherein a product is placed into a polyestercontainer by employing the polyesters described herein as the polyestersfrom which the container is formed. Thus for example all that isrequired is to form an appropriate container of the polyesterscontemplated herein and then using that container to package foodstuffs,beverages, medicines, and the like.

The present polyesters can be melt molded into containers, for examplebottles, and these containers will be clear i.e., to the unaided eye thecontainer will be transparent thereby allowing for the visualobservation of the packaged product through the container walls. Inpassing it should be mentioned that when the term melt-molded isemployed herein this contemplates conventional known processes whereinthermoplastic materials, for example polyethylene terephthalate, arefirst taken to a melt state and then molded for example by blow moldingtechniques, or injection molding techniques, or combinations thereof,into a final container or bottle. Thus for example the presentpolyesters can be melt molded into bottles or jars by techniqueswherein, for example, a parison is first formed by a blow molding, orinjection molding, operation and wherein the parison is biaxiallystretched or oriented and formed into a final configuration, again forexample, by blow molding. Thus copolyesters as contemplated in thepresent invention may be melt molded to clear bottles and containers foruse in the packaging industry using any of the techniques known in theart for forming melt molded containers.

While the foregoing describes the present invention with sufficientparticularity to enable those skilled in the art to make and use samethere nonetheless follows, for exemplary purposes only, a specificexample.

EXAMPLE I

A polyester was prepared having the following repeating units in itsbackbone: ##STR3## Based on the proportions of the polyester formingprecursors used in the reaction the mole ratio of b:a was about 50:50and the mole ratio of c:d was 80:20. The specific charge of ingredients,or precursors, was about 0.0386 moles of dimethyl sulfonyldibenzoate,about 0.0386 moles of dimethyl terephthalate, about 0.1544 moles ofethylene glycol, and about 0.0386 moles of neopentyl glycol(2,2-dimethyl-1,3-propanediol). For catalytic purposes the charge alsoincluded about 8.47 milligrams of Zn(C₂ H₃ O₂)₂ ·2H₂ O and about 4.26milligrams of Sb₂ O₃.

The mixture of the starting materials were weighed into a 300 ml,3-necked round bottom flask equipped with a stirrer, nitrogen inlettube, and a condenser. The contents of the flask were heated at about195° to about 205° C. for 3 hours with nitrogen flowing into thereaction flask to provide a nitrogen blanket. About 80% of thetheoretical methanol by-product was removed. After this 3 hour period at195° to 205° C. the contents were then heated to about 260° C. and avacuum of about 24 mm Hg was applied and the system held for about 1hour. Ethylene glycol, neopentyl glycol and by product methanol wasremoved. The condensation of the prepolymer polyester was then continuedat a temperature of about 285° to about 295° C. and was maintained therefor a period of about 3-4 hours under a vacuum of about 0.5 millimetersof mercury. During this time excess ethylene glycol and neopentyl glycolwere further removed by distillation. After this period the polymer wasremoved and found to have a glass transition temperature, as measuredwith a Differential Scanning Calorimeter, of about 117° C., and anoxygen permeability, as measured by ASTM D-1434-66, of about 8.9cc.mil/100 in.² ·day·atm. at about 73° F. and 50% relative humidity anda CO₂ permeability of about 58.6 cc.mil/100 in.² ·day·atm. and a watervapor transmission of about 1.46 (ASTM-E-96-66). The polymer was easilyformed into a flexible clear film, and had an inherent viscosity of 0.57(0.25% polymer in a 60/40 weight percent solution of tetrachloroethaneand phenol).

Following the known forming procedures of the prior art, e.g. U.S. Pat.No. 3,733,309, a biaxially oriented container (i.e. a container having abottom wall and a circumferential sidewall merging with and proceedingupwardly from the bottom wall, the sidewall at its upper margin taperinginwardly and merging with a neck portion defining a mouth opening) isformed from the above-produced polyester of this invention. Thiscontainer is clear and upon being filled by placing foodstuffs,beverages, medicines and the like therein and closing the containershows excellent characteristics for packaging of such products. Asimilar bottle, but one which is not oriented also shows excellentcharacteristics for packaging but is weaker.

In a similar manner a polyester was produced using the polyestersynthesis procedure as above but without any dimethyl terephthalate.That is the ratio of c:d was about 80:20 and the ratio of b:a was 0:100.The polyester had a glass transition temperature of about 137° C. butits permeability characteristics are unsatisfactory (O₂ = 20.3 and CO₂ =147).

I claim:
 1. A linear copolyester which can be melted and molded to aclear container, the repeating units of said polyester consistingessentially of ##STR4## said polyester having an oxygen permeability ofless than 15 cc.mil/100 in.² ·day·atm. and a glass transitiontemperature in excess of 72° C., said (a) and (b) units and said (c) and(d) units respectively being the units formed by reactively combiningpolyester forming precursors thereof in an amount of at least one moleof the precursors of said (c) and (d) units per mole of precursors ofsaid (a) and (b) units and wherein the precursors of said units informing said polyester by said reactive combining are in a molar ratioof said (b) unit precursor to said (a) unit precursor of about 90:10 toabout 40:60 and a molar ratio of said (c) unit precursor to said (d)unit precursor of about 80:20.
 2. The copolyester of claim 1 whereinsaid precursor ratio of (b) to (a) units is about 50:50, saidcopolyester having an oxygen permeability of about 9 and a glasstransition temperature of about 117° C.
 3. In a method of forming apolyester by reactively combining at least one polyester formingdicarboxylic acid, ester or halide thereof with at least astoichiometric amount of at least one polester forming dibasic alcohol,under conditions of temperature, pressure and catalysis so as to form apolyester, the improvement wherein said acid, ester or halide consistsessentially of (1) p,p'-sulfonyldibenzoic acid, esters thereof, orhalides thereof and (2) terephthalic acid, esters thereof, or halidesthereof, and wherein said alcohol consists essentially of (3) ethyleneglycol and (4) neopentyl alcohol, the mole ratio of (2) to (1) beingabout 90:10 to about 40:60 and the mole ratio of (3) to (4) being about80:20.